is (Chemical Oxygen Demand) chemical oxygen demand. Chemical oxygen demand (COD) discharge is the sum of COD discharge in industrial wastewater and COD discharge in domestic sewage. Chemical oxygen demand refers to the amount of oxygen required to oxidize organic pollutants in water with chemical oxidants. Generally, chemical oxidants are used to oxidize and decompose oxidizable substances (organic matter, nitrite, ferrous salt, sulfide, etc.) in wastewater, and then calculate the oxygen consumption according to the amount of residual oxidant to represent the content of organic matter in wastewater , reflecting the degree of organic matter pollution in the water body. The higher the COD value, the heavier the pollution of organic pollutants in the water. The following is the method for monitoring COD value of species introduced by water quality online analyzer manufacturers and everyone. 1. The COD online analyzer dichromate method (more accurate) The standard method for the determination of chemical oxygen demand is based on the Chinese standard GB11914 'Determination of water quality chemical oxygen demand by dichromate method' and the standard ISO6060 'Water quality chemical oxygen demand As a representative of the method, the method has high oxidation rate, good reproducibility, accuracy and reliability, and has become a classic standard method generally recognized by the society. The measurement principle is: in H2SO4 acidic medium, potassium dichromate is used as oxidant, H2SO4 silver is used as catalyst, H2SO4 mercury is used as a masking agent for chloride ions, the acidity of H2SO4 in the digestion reaction solution is 9mol/L, and the digestion reaction solution is boiled by heating. 148°C; the boiling point temperature of 2°C is the digestion temperature. 2. Potassium permanganate method Potassium permanganate is used as an oxidant to measure COD, and the measured value is called potassium permanganate index. 3. The spectrophotometric method is based on the classic standard method. Potassium dichromate oxidizes organic substances, and hexavalent chromium generates trivalent chromium. The relationship between the absorbance value of hexavalent chromium or trivalent chromium and the COD value of water samples is used to determine Water sample COD value. 4. Rapid digestion method The classic standard method is the reflux 2h method. In order to improve the analysis speed, various rapid analysis methods have been proposed. There are mainly two methods: one is to increase the concentration of oxidant in the digestion reaction system, increase the acidity of H2SO4, increase the reaction temperature, and increase the co-catalyst and other conditions to increase the reaction rate. 5. Spectrophotometric chemical oxygen demand (COD) determination method, whether it is reflux volume method, fast method or photometric method, uses potassium dichromate as the oxidant, H2SO4 silver as the catalyst, and H2SO4 mercury as the masking agent for chloride ions. Determination method based on COD digestion system in H2SO4 acidic condition.
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